Culex pipiens mosquito is a major vector species for Japanese encephalitis and filariasis in China, and it is an important vector of West Nile Virus in the USA. Vector control is an important means of mosquito-borne disease prevention and management. Pyrethroid insecticides are currently being promoted worldwide for disease vector control because of their high efficacy, rapid rate of knockdown, and low mammalian toxicity. Due to wide-spread and improper use of insecticides, resistance to pyrethroids has been reported in Culex pipiens mosquito species in China. Insecticide resistance represents a major obstacle in the struggle against vector-borne disease. The long-term goal of this research is to elucidate the genetic and molecular mechanisms of pyrethroid resistance in Culex pipiens pallens mosquitoes, and to develop more accurate and cost-effective resistance detection methods that are applicable to field samples. We have previously characterized several genes differentially expressed in pyrethroid-resistant Culex pipiens pallens mosquitoes. Because all functional analyses of the differentially expressed genes were previously conducted on mosquito cell lines, a complementary approach using whole mosquitoes is critical to reveal the genetic basis of insecticide resistance at organism level. Insecticide resistance research at the organism level is important because mosquitoes may possess compensatory mechanisms under the selection by insecticides. Studying individual genes in cell lines will not reveal gene-environment interactions. Accordingly, this research will use population genetic approach and molecular methods to determine the genetic and molecular mechanisms of Culex pipiens pallens mosquito resistance to deltamethrin, a synthetic pyrethroid insecticide. The specific aims are: 1) to conduct quantitative trait loci mapping on Culex pipiens pallens resistance to deltamethrin insecticide;2) to identify putative candidate genes and analyze the role of the candidate genes in resistance to deltamethrin;and 3) to develop molecular, biochemical or immunological-based methods for the detection of deltamethrin resistance in Culex pipiens pallens. This research will lead to the development of new tools for the monitoring and management of insecticide resistance in Culex mosquitoes, and provide critical information on the selection of appropriate insecticides in vector control. This research is timely because pyrethroids are currently being used extensively worldwide as a part of global efforts to control mosquito-borne diseases, and pyrethroid resistance is seriously impeding the efficacy of mosquito control in China. PUBLIC HEALTH RELEVANCE: Culex pipiens is a major vector species for Japanese encephalitis and filariasis in China, and it is an important vector of West Nile Virus in the USA. Insecticide-based mosquito control is an important method, but Insecticide resistance represents a major obstacle in the struggle against vector-borne disease. This project will better understand the genetic mechanisms of resistance to pyrethroid insecticide in Cx. pipiens pallens mosquitoes, and will lead to novel diagnosis methods for resistance. Thus, the proposed research will greatly enhance the monitoring and management of insecticide resistance.